Reconfigurable fixture device and methods of use

ABSTRACT

A process generally includes contacting a surface of at least one workpiece with a reconfigurable pad of a fixture device, wherein the reconfigurable pad comprises a shape memory material configured to conform to the surface of the at least one workpiece, and fixturing the contacted workpiece.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application relates to, and claims the benefit of, U.S.Provisional Patent Application No. 60/645,263, which was filed on Jan.19, 2005 and is incorporated herein in its entirety.

BACKGROUND

The present disclosure generally relates to a flexible manufacturingsystem and, more particularly, to a reconfigurable fixture device forclamping and/or providing support for a variety of different workpiececonfigurations.

The advent of assembly lines has enabled rapid, mass production ofproducts at a reduced product cost. Assembly lines typically includemultiple operation stages and component, material, or sub-assemblyinputs. Sometimes the workpieces are similar or related part shapes.Other times, the workpieces are of unrelated design but require similarmanufacturing operations. In these varied applications, the fixturereconfiguration or changeover from one part design to another has to befast enough to meet the productivity requirements of currentmanufacturing systems.

Previous efforts in designing and developing flexible fixturing foreither small batch manufacture or mass production scenarios cangenerally include the use of modular fixtures and conformable fixtures.Modular fixturing generally includes fixtures assembled from a standardlibrary of elements such as V-blocks, toggle clamps, locating blocks,and the like. Their flexibility lies in the ability to be reconfiguredeither manually or by a robotic device. However, modular fixtures haveno intrinsic ability to adapt to different sizes and shapes of partswithin a part family. In addition, the time necessary forreconfiguration is long. As a result, modular fixtures are more suitedto a job shop environment than mass production.

The advent of Flexible Manufacturing Systems (FMS) in the early 1960'sprovided the impetus for work on conformable fixturing. A conformablefixture is defined as one that can be configured to accept parts ofvarying shape and size. Conformable fixture technology generallyincludes encapsulant or mechanistic techniques. Examples of encapsulantfixtures are found in the aerospace industry, where low melting-pointmetals are used to enclose turbine blades and produce well-definedsurfaces for part location and clamping for grinding operations. Whilean excellent means of facilitating the holding of complex parts,encapsulation is a costly and time-consuming process.

Mechanistic fixtures reported in the literature include the use of petalcollets, programmable conformable clamps, a programmable/multi-leafvise, and an adjustable integral fixture pallet. Of the four, theadjustable integral fixture pallet concept appears to be the mostcapable of accommodating a part family of castings. To date, however nofeasibility studies have been conducted regarding the applicability ofany of these techniques to production machining operations.

One troublesome area in flexible manufacturing systems is itsimplementation in body shops. Clamps are typically employed to clamp thevarious sheet metal workpieces (e.g., body panels) during assembly andclamping can potentially scratch the exposed surface and/or locallydeform the workpiece or surface coating, affecting its aestheticquality. While, ideally, clamping could be performed on flanges orsurfaces that are invisible or immaterial to end users, some clampinginevitably occurs on surfaces whose quality is important aesthetically.

Current clamps utilized in assembly lines generally include a metal(e.g., tool steel) clamp block, which accurately matches the contours ofthe workpiece and a matching pressure foot. In operation, the clampblock with a contoured surface supports the exterior surface of theworkpiece while the pressure foot contacts the inner (non-exposed)surface. As a result, the contour of each clamp block is generallyspecific to a limited number of workpieces. In dedicated facilities, thecontours of the clamp block are generally fabricated by numericallycontrolled (NC) machining using data generated from the workpiece to befixtured. A problem arises if multiple models having significantlydifferent workpiece configurations are to be produced on the sametooling setup. Multiple clamp blocks having different contours are thenrequired to accommodate the multiplicity of workpiece configurations.

Clamps with a compliant pad and a matching pressure foot are also usedin assembly lines for fixturing workpieces with aesthetically importantsurfaces. In operation, the clamp block with a contoured surfacesupports the exterior surface of the workpiece while the pressure footcontacts the inner (non-exposed) surface. The compliance of the clampblock ensures that the surface is not marked and the rigidity of thepressure foot ensures that the location of the part is known completely(to within the tolerance imposed by the deformation of the part underthe clamp loads), i.e., the part is not floating with regard to theclamp block. With this approach, minor differences between the shape ofthe workpiece and the clamp block geometry can be accommodated withoutintroducing local deformation. As a result, the contour of each clampblock is generally specific to a limited number of workpieces. Indedicated facilities, the contours of the clamp block are generallyfabricated by numerically controlled (NC) machining using data generatedfrom the workpiece to be fixtured. A problem arises if multiple modelsare produced having significantly different workpiece configurations.Multiple clamp blocks having different contours are then required toaccommodate the multiplicity of workpiece configurations.

Accordingly, there remains a need for a reconfigurable fixture devicethat can provide adequate support and/or clamping means for a variety ofworkpiece configurations.

BRIEF SUMMARY

Disclosed herein are processes related to a reconfigurable fixturedevice for clamping and/or providing support for a variety of differentworkpiece configurations. In one embodiment, a process generallyincludes contacting a surface of at least one workpiece with areconfigurable pad of a fixture device, wherein the reconfigurable padcomprises a shape memory material configured to conform to the surfaceof the at least one workpiece and fixturing the contacted workpiece.

In another embodiment, a process includes contacting a first surface ofa first workpiece with a reconfigurable pad of a fixture device, whereinthe reconfigurable pad comprises a shape memory material configured toconform to the first surface of the first workpiece; fixturing thecontacted first workpiece; conforming the reconfigurable pad of thefixture device to a second surface of a second workpiece; contacting thesecond surface of the second workpiece with the reconfigurable pad ofthe fixture device; and fixturing the second workpiece.

In yet another embodiment, a process for conforming a reconfigurable padof a fixture device to a surface of at least one workpiece comprisesheating the reconfigurable pad effective to increase a temperature of ashape memory material to or above a shape setting temperature; applyinga force to the reconfigurable pad effective to deform the reconfigurablepad from an original shape to a shape conforming to the surface of theat least one workpiece; and cooling the shape memory material below theshape setting temperature.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments andwherein the like elements are numbered alike:

FIG. 1 is a cross sectional view of a fixture device prior to settingthe configuration of the reconfigurable pad;

FIG. 2 is a cross sectional view of the fixture device of FIG. 1 duringthe setting of the configuration of the reconfigurable pad so as toconform to a surface of a workpiece;

FIG. 3 is a cross sectional view of the fixture device of FIG. 1 uponremoval of the workpiece after setting the configuration of thereconfigurable pad;

FIG. 4 is a cross sectional view of the fixture device of FIG. 1 afterresetting the reconfigurable pad to its original configuration;

FIG. 5 is a cross sectional view of a fixture device with a compositereconfigurable pad;

FIG. 6 is a cross sectional view of a fixture device adapted forgripping and/or clamping a workpiece, wherein the respectivereconfigurable pads are set to conform to the surface of the workpiece;

FIG. 7 is a cross sectional view of the fixture device of FIG. 6 uponrelease of the workpiece;

FIG. 8 is a cross sectional view of a fixture device employing athermoelectric unit in accordance with one embodiment; and

FIG. 9 is a cross sectional view of a fixture device employing athermoelectric unit in accordance with another embodiment.

DETAILED DESCRIPTION

Disclosed herein are reconfigurable fixture devices for providingsupport and/or securement of a variety of dissimilar workpieces such asmay be desired for a flexible manufacturing system. Suitable workpiecesfor loading onto the fixture device are those that are sufficientlyrigid so as not to flex or distort under the weight of the workpiece orby any clamping force (which can be as high as 500 pounds distributedover roughly 1 square inch) when using the fixture device. Althoughreference will be made to its use in fixturing body panels for motorvehicles (e.g., cars, trucks, motorcycles, boats, airplanes, and thelike), it should be understood that the reconfigurable fixture devicescould be employed for a variety of end use applications where it may bedesirable to support and/or clamp dissimilar workpieces using the sametooling setup without requiring manual adjustment or reprogramming. Forexample, the reconfigurable fixture devices can be employed forfixturing thin walled and/or thick walled objects, contoured and/orplanar objects, on exterior surfaces as well as on hidden surfaces, andthe like.

It will be apparent to those skilled in the art in view of thisdisclosure that the reconfigurable fixture devices disclosed herein canadvantageously be used on exposed surfaces of body panels withoutmarring, scratching, and/or causing local deformations such as may berequired for assembly of parts having Class A surfaces. Class A surfacesare generally external surfaces that are visible to an end user (e.g., adoor, fender, hood, trunk, hull, interior trim, and the like). Incontrast, Class B and C surfaces are generally surfaces not normallyseen by the end user and have fewer requirements in terms of tangencyand surface defects.

Referring now to FIGS. 1-9, there are shown cross-sectional views ofexemplary reconfigurable fixture devices, generally designated byreference numeral 10, in varying types and/or stages of fixturing. Thereconfigurable fixture device 10 can be employed as a supporting device(e.g., as shown in FIGS. 1-5 and 8-9) or as a clamping device (e.g., asshown in FIGS. 6-7) depending on the desired application. As such, theterm “fixture device” includes devices intended for clampingapplications as well as for supporting applications.

Also, the terms “first”, “second”, and the like do not denote any orderor importance, but rather are used to distinguish one element fromanother, and the terms “the”, “a”, and “an” do not denote a limitationof quantity, but rather denote the presence of at least one of thereferenced items. Furthermore, all ranges reciting the same quantity orphysical property are inclusive of the recited endpoints andindependently combinable.

The reconfigurable fixture device 10 for clamping and/or supportingworkpieces 16 generally includes a base member 12 upon which is disposeda reconfigurable pad 14. The fixture device 10 can be fixed in spacesuch as by hard tooling or may be adapted for use with programmablemulti-axis tooling device (e.g., robotics, and the like). In supportingapplications (i.e., FIGS. 1-5 and 8-9), the fixture device 10 includes a(i.e., at least one) reconfigurable pad 14, which can be utilized duringprocessing to support the workpiece. Alternatively, in clampingapplications (FIGS. 6-7), a (i.e., at least one) pair of opposing pads(e.g., one for a clamp block and one for an opposing pressure foot) areemployed, wherein one or both of the pads are reconfigurable in themanner that will be described in greater detail below. For example, afixture device can be employed for clamping a workpiece 16 in which onlythe pad contacting the Class-A surface of the workpiece isreconfigurable while the opposing pad that contacts a non-Class Asurface is not. In other clamping application embodiments, such as thoseshown in FIGS. 6-7, it may be desirable that both pads arereconfigurable.

Hereinbelow, for convenience, when reference is made to a reconfigurablepad 14, the reconfigurable pad 14 being described may be thereconfigurable pad 14 used for a supporting fixture device 10 and/or itmay be one or both (depending on the application) of the opposingreconfigurable pads 14 used for a clamping fixture device 10.

Optionally, the base member 12 may have a plurality of reconfigurablepads 14 disposed thereupon. One or more than one of the plurality ofreconfigurable pads 14 may be used to fixture a single workpiece 16 atthe same time. In one embodiment, each of the reconfigurable pads 14 isindexed (i.e., each of the plurality of reconfigurable pads 14 can beconfigured to a specific range of workpiece 16 shapes) and the basemember 12 may be rotated or moved to place the appropriately indexedreconfigurable pad 14 in position to fixture the workpiece 16.

Optionally, the fixture device 10 further comprises a locator pin 15disposed on the base member 12, within and/or adjacent to thereconfigurable pad 14. The locator pin 15 desirably remains in a fixedposition with respect to the base member 12. The locator pin 15 can beused to provide information as to the location of the workpiece 16during operation of the fixture device 10.

The base member 12 can be constructed of any material onto which thereconfigurable pad 14 can be disposed, and which can withstand at leasta portion of the weight of the workpiece 16. For example, the basemember may be formed from a metal, alloy, ceramic, and the like.

The reconfigurable pad 14 comprises a shape memory material that isadapted to selectively conform to a surface contour of the workpiece 16disposed thereon in response to an activation signal. Advantageously,the reconfigurable pad 14 can be restored to its original shape as maybe desired as well as be reconfigured to accept a different workpiece 16surface contour, thereby providing versatility to the fixture device 10and overcoming the problems noted in the prior art. Optionally, thereconfigurable pad 14 may be thermally insulated from the tooling (i.e.,base member 12) that it is mounted on and/or a training surface or workpiece (e.g. 16) to avoid the quenching influence of any associatedthermal mass. An alternative to insulating the reconfigurable pad 14from the training surface (i.e., to which the reconfigurable pad 14 willconform) is to maintain the training surface at the training orconforming temperature (T_(t)) during the training (i.e., shape settingor conforming) step as will be described in greater detail below.

The reconfigurable pad 14 can be of any shape or size, provided that itcan selectively conform to the surface contour of the workpiece 16. Forexample, the reconfigurable pad may be a dense solid (e.g., box- ordisc-shaped), perforated or porous, hollow (e.g., so as to form achamber), granular, or the like.

Because the reconfigurable pad 14 can be adapted to substantiallyconform to any workpiece 16 surface contour, the fixture device 10 canbe employed for a variety of different workpieces 16, therebyrepresenting a significant commercial advantage in, for example, aflexible manufacturing system that traditionally employed multipleclamps and clamp/supporting member pads specific to individualworkpieces 16. For example, significant savings can be obtained byreducing design, engineering, manufacturing, and purchasing of fixturedevices for each product type (e.g., dissimilar body panels).

Shape memory materials generally refer to materials or compositions thathave the ability to remember their original shape, which cansubsequently be recalled by applying an external stimulus (i.e., anactivation signal). As such, deformation of the shape memory materialfrom the original shape can be a temporary condition, which can be usedfor fixturing a variety of workpieces 16 having different surfacecontours. Exemplary shape memory materials include shape memory alloys(SMAs), shape memory polymers (SMPs), shape memory ceramics (SMCs),baroplastics, composites of the foregoing shape memory materials withnon-shape memory materials, and combinations comprising at least one ofthe foregoing shape memory materials. For convenience and by way ofexample, reference herein will be made to shape memory alloys and shapememory polymers. The shape memory ceramics, baroplastics, and the likecan be employed in a similar manner as will be appreciated by thoseskilled in the art in view of this disclosure. For example, withbaroplastic materials, a pressure induced mixing of nanophase domains ofhigh and low glass transition temperature (Tg) components effects theshape change. Baroplastics can be processed at relatively lowtemperatures repeatedly without degradation. SMCs are similar to SMAsbut can tolerate much higher operating temperatures than can othershape-memory materials. An example of an SMC is a piezoelectricmaterial.

Shape memory alloys are alloy compositions with at least two differenttemperature-dependent phases. The most commonly utilized of these phasesare the so-called martensite and austenite phases. In the followingdiscussion, the martensite phase generally refers to the moredeformable, lower temperature phase whereas the austenite phasegenerally refers to the more rigid, higher temperature phase. When theshape memory alloy is in the martensite phase and is heated, it beginsto change into the austenite phase. The temperature at which thisphenomenon starts is often referred to as austenite start temperature(A_(s)). The temperature at which this phenomenon is complete is calledthe austenite finish temperature (A_(f)). When the shape memory alloy isin the austenite phase and is cooled, it begins to change into themartensite phase, and the temperature at which this phenomenon starts isreferred to as the martensite start temperature (M_(s)). The temperatureat which austenite finishes transforming to martensite is called themartensite finish temperature (M_(f)). It should be noted that theabove-mentioned transition temperatures are functions of the stressexperienced by the SMA sample. Specifically, these temperatures increasewith increasing stress. In view of the foregoing properties, deformationof the shape memory alloy is preferably at or below the austenitetransition temperature (at or below A_(s)). Subsequent heating above theaustenite transition temperature causes the deformed shape memorymaterial sample to revert back to its permanent shape. Thus, a suitableactivation signal for use with shape memory alloys is a thermalactivation signal having a magnitude that is sufficient to causetransformations between the martensite and austenite phases.

The temperature at which the shape memory alloy remembers its hightemperature form when heated can be adjusted by slight changes in thecomposition of the alloy and through thermo-mechanical processing. Innickel-titanium shape memory alloys, for example, it can be changed fromabove about 100° C. to below about −100° C. The shape recovery processcan occur over a range of just a few degrees or exhibit a more gradualrecovery. The start or finish of the transformation can be controlled towithin a degree or two depending on the desired application and alloycomposition. The mechanical properties of the shape memory alloy varygreatly over the temperature range spanning their transformation,typically providing shape memory effect, superelastic effect, and highdamping capacity. For example, in the martensite phase a lower elasticmodulus than in the austenite phase is observed. Shape memory alloys inthe martensite phase can undergo large deformations by realigning thecrystal structure arrangement with the applied stress, e.g., pressurefrom a matching pressure foot. As will be described in greater detailbelow, the material will retain this shape after the stress is removed.

Suitable shape memory alloy materials for fabricating theclamp/supporting member pad include, but are not intended to be limitedto, nickel-titanium based alloys, indium-titanium based alloys,nickel-aluminum based alloys, nickel-gallium based alloys, copper basedalloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold,and copper-tin alloys), gold-cadmium based alloys, silver-cadmium basedalloys, indium-cadmium based alloys, manganese-copper based alloys,iron-platinum based alloys, iron-palladium based alloys, and the like.The alloys can be binary, ternary, or any higher order so long as thealloy composition exhibits a shape memory effect, e.g., change in shape,orientation, yield strength, flexural modulus, damping capacity,superelasticity, and/or similar properties. Selection of a suitableshape memory alloy composition depends on the temperature range wherethe component will operate.

Reference will now be made to a reconfigurable pad 14 formed of an SMA.To train/set the shape so as to accommodate the contour of the workpiece16, the reconfigurable pad 14 is pressed against the workpiece 16 with aforce (F₁) that causes the stresses in the reconfigurable pad 14 toexceed the first yield point of the martensite phase. It should beunderstood that training or setting the shape of the reconfigurable padcan be done using a so-called “master” article with a shapesubstantially similar to the workpiece. This master article may be aprogrammable device that can generate many different surface contours(e.g. a bed-of-nails, wherein the position of each of the nails isprogrammable).

The SMA can be in the form of a foam or other structure as may bedesired for the particular application, e.g., springs, bands, laminates,and the like, and is not intended to be limited to any particular formor shape. The SMA in the martensite phase undergoes a large, seeminglyplastic deformation, at a nearly constant stress. This allows thereconfigurable pad 14 to deform freely in order to conform to thecontours of the workpiece 16, as shown in FIG. 2. When the trainingforce (i.e., setting force) is removed, the reconfigurable pad 14 willretain most, if not all, of the deformation produced during the trainingstep, as illustrated in FIG. 3. A small part of the induced deformationmay be lost due to elastic recovery.

Although reference has been made to a reconfigurable pad 14 formed of anSMA in the martensite phase, it should be understood that training couldoccur with a reconfigurable pad 14 formed of the SMA in the austenitephase. In this manner, the SMA behaves similar to a high stiffnessrubber-like material. The SMA plastically deforms during the trainingstep as a result of a stress-induced austenite to martensitetransformation so as to conform to the workpiece 16 surface. However,unlike the martensitic SMA described in the previous paragraph, theaustenitic SMA reconfigurable pad 14 does not retain the deformationinduced in it after the training force is removed. Hence, thisreconfigurable pad 14 has to be trained for each workpiece 16 of adifferent shape.

One or more fixture devices 10 with a contoured (i.e., trained)reconfigurable pad 14 are then used to fixture the workpiece 16 in amanner that distributes the reaction force over a large area, and thus,minimizes the possibility of darnaging the surface of the workpiece 16.The fixturing force (F₂), which is either a support force or a clampforce, during regular use of the reconfigurable pad(s) 14 should,generally, be smaller than F₁ such that the stresses induced by F₂ donot exceed the first yield point of the martensite phase. Fixturingforces during regular use that are significantly higher than thetraining forces are also possible if the training step is continued to apoint where the stress in the reconfigurable pad(s) 14 increases beyondthe first yield point but not beyond the second yield point of themartensite phase SMA. However, it should be noted that the latterapproach requires closer control, both during the training step andduring regular use to ensure that the conformity between thereconfigurable pad(s) 14 and the support surface on the workpiece 16 isnot compromised.

The reconfigurable pad 14 might optionally undergo a reset step beforethey are reconfigured for fixturing a workpiece 16 at a location with adifferent surface geometry. In the reset step, the reconfigurable pad 14is unloaded and heated to a temperature above the austenite-finishtemperature of the SMA, and cooled back to the ambient or workingtemperature as desired. Heating the reconfigurable pad 14 to atemperature above the austenite finish temperature produces a martensiteto austenite phase transformation that is accompanied by completerecovery of the seemingly plastic deformation induced during thetraining step (see FIG. 4) provided that the reconfigurable pad 14 isunloaded, the recovery is not constrained in any manner and sufficienttime is allowed for the process. This recovery restores thereconfigurable pad 14 to its original (i.e., undeformed) configuration,which is retained even after it has been cooled. The training process isthen repeated for the new workpiece 16 surface geometry. Alternatively,the reconfigurable pad 14 can be trained for the new surface contourdirectly as opposed to resetting to the original shape(s).

As previously mentioned, other suitable shape memory materials for usein the reconfigurable pad 14 are shape memory polymers (SMPs). “Shapememory polymer” generally refers to a polymeric material, which exhibitsa change in a property, such as an elastic modulus, a shape, adimension, a shape orientation, or a combination comprising at least oneof the foregoing properties upon application of an activation signal.Shape memory polymers may be thermoresponsive (i.e., the change in theproperty is caused by a thermal activation signal), photoresponsive(i.e., the change in the property is caused by a light-based activationsignal), moisture-responsive (i.e., the change in the property is causedby a liquid activation signal such as humidity, water vapor, or water),or a combination comprising at least one of the foregoing.

Generally, SMPs are phase segregated co-polymers comprising at least twodifferent units, which may be described as defining different segmentswithin the SMP, each segment contributing differently to the overallproperties of the SMP. As used herein, the term “segment” refers to ablock, graft, or sequence of the same or similar monomer or oligomerunits, which are copolymerized to form the SMP. Each segment may becrystalline or amorphous and will have a corresponding melting point orglass transition temperature (Tg), respectively. The term “thermaltransition temperature” is used herein for convenience to genericallyrefer to either a Tg or a melting point depending on whether the segmentis an amorphous segment or a crystalline segment. For SMPs comprising(n) segments, the SMP is said to have a hard segment and (n−1) softsegments, wherein the hard segment has a higher thermal transitiontemperature than any soft segment. Thus, the SMP has (n) thermaltransition temperatures. The thermal transition temperature of the hardsegment is termed the “last transition temperature”, and the lowestthermal transition temperature of the so-called “softest” segment istermed the “first transition temperature”. It is important to note thatif the SMP has multiple segments characterized by the same thermaltransition temperature, which is also the last transition temperature,then the SMP is said to have multiple hard segments.

When the SMP is heated above the last transition temperature, the SMPmaterial can be imparted a permanent shape. A permanent shape for theSMP can be set or memorized by subsequently cooling the SMP below thattemperature. As used herein, the terms “original shape”, “previouslydefined shape”, and “permanent shape” are synonymous and are intended tobe used interchangeably. A temporary shape can be set by heating thematerial to a temperature higher than a thermal transition temperatureof any soft segment yet below the last transition temperature, applyingan external stress or load to deform the SMP, and then cooling below theparticular thermal transition temperature of the soft segment whilemaintaining the deforming external stress or load.

The permanent shape can be recovered by heating the material, with thestress or load removed, above the particular thermal transitiontemperature of the soft segment yet below the last transitiontemperature. Thus, it should be clear that by combining multiple softsegments it is possible to demonstrate multiple temporary shapes andwith multiple hard segments it may be possible to demonstrate multiplepermanent shapes. Similarly using a layered or composite approach, acombination of multiple SMPs will demonstrate transitions betweenmultiple temporary and permanent shapes.

For SMPs with only two segments, the temporary shape of the shape memorypolymer is set at the first transition temperature, followed by coolingof the SMP, while under load, to lock in the temporary shape. Thetemporary shape is maintained as long as the SMP remains below the firsttransition temperature. The permanent shape is regained when the SMP isonce again brought above the first transition temperature with the loadremoved. Repeating the heating, shaping, and cooling steps canrepeatedly reset the temporary shape.

Most SMPs exhibit a “one-way” effect, wherein the SMP exhibits onepermanent shape. Upon heating the shape memory polymer above a softsegment thermal transition temperature without a stress or load, thepermanent shape is achieved and the shape will not revert back to thetemporary shape without the use of outside forces.

As an alternative, some shape memory polymer compositions can beprepared to exhibit a “two-way” effect, wherein the SMP exhibits twopermanent shapes. These systems include at least two polymer components.For example, one component could be a first cross-linked polymer whilethe other component is a different cross-linked polymer. The componentsare combined by layer techniques, or are interpenetrating networks,wherein the two polymer components are cross-linked but not to eachother. By changing the temperature, the shape memory polymer changes itsshape in the direction of a first permanent shape or a second permanentshape. Each of the permanent shapes belongs to one component of the SMP.The temperature dependence of the overall shape is caused by the factthat the mechanical properties of one component (“component A”) arealmost independent of the temperature in the temperature interval ofinterest. The mechanical properties of the other component (“componentB”) are temperature dependent in the temperature interval of interest.In one embodiment, component B becomes stronger at low temperaturescompared to component A, while component A is stronger at hightemperatures and determines the actual shape. A two-way memory devicecan be prepared by setting the permanent shape of component A (“firstpermanent shape”), deforming the device into the permanent shape ofcomponent B (“second permanent shape”), and fixing the permanent shapeof component B while applying a stress.

It should be recognized by one of ordinary skill in the art that it ispossible to configure SMPs in many different forms and shapes.Engineering the composition and structure of the polymer itself canallow for the choice of a particular temperature for a desiredapplication. For example, depending on the particular application, thelast transition temperature may be about 0° C. to about 300° C. orabove. A temperature for shape recovery (i.e., a soft segment thermaltransition temperature) may be greater than or equal to about −30° C.Another temperature for shape recovery may be greater than or equal toabout 40° C. Another temperature for shape recovery may be greater thanor equal to about 100° C. Another temperature for shape recovery may beless than or equal to about 250° C. Yet another temperature for shaperecovery may be less than or equal to about 200° C. Finally, anothertemperature for shape recovery may be less than or equal to about 150°C.

Optionally, the SMP can be selected to provide stress-induced yielding,which may be used directly (i.e. without heating the SMP above itsthermal transition temperature to ‘soften’ it) to make the pad conformto a given surface. The maximum strain that the SMP can withstand inthis case can, in some embodiments, be comparable to the case when theSMP is deformed above its thermal transition temperature.

Although reference has been, and will further be, made tothermoresponsive SMPs, those skilled in the art in view of thisdisclosure will recognize that photoresponsive, moisture-responsive SMPsand SMPs activated by other methods may readily be used in addition toor substituted in place of thermoresponsive SMPs. For example, insteadof using heat, a temporary shape may be set in a photoresponsive SMP byirradiating the photoresponsive SMP with light of a specific wavelength(while under load) effective to form specific crosslinks and thendiscontinuing the irradiation while still under load. To return to theoriginal shape, the photoresponsive SMP may be irradiated with light ofthe same or a different specific wavelength (with the load removed)effective to cleave the specific crosslinks. Similarly, a temporaryshape can be set in a moisture-responsive SMP by exposing specificfunctional groups or moieties to moisture (e.g., humidity, water, watervapor, or the like) effective to absorb a specific amount of moisture,applying a load or stress to the moisture-responsive SMP, and thenremoving the specific amount of moisture while still under load. Toreturn to the original shape, the moisture-responsive SMP may be exposedto moisture (with the load removed).

Suitable shape memory polymers, regardless of the particular type ofSMP, can be thermoplastics, thermosets-thermoplastic copolymers,interpenetrating networks, semi-interpenetrating networks, or mixednetworks. The SMP “units” or “segments” can be a single polymer or ablend of polymers. The polymers can be linear or branched elastomerswith side chains or dendritic structural elements. Suitable polymercomponents to form a shape memory polymer include, but are not limitedto, polyphosphazenes, poly(vinyl alcohols), polyamides, polyimides,polyester amides, poly(amino acid)s, polyanhydrides, polycarbonates,polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols,polyalkylene oxides, polyalkylene terephthalates, polyortho esters,polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters,polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers,polyether amides, polyether esters, and copolymers thereof. Examples ofsuitable polyacrylates include poly(methyl methacrylate), poly(ethylmethacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate),poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(laurylmethacrylate), poly(phenyl methacrylate), poly(methyl acrylate),poly(isopropyl acrylate), poly(isobutyl acrylate) andpoly(octadecylacrylate). Examples of other suitable polymers includepolystyrene, polypropylene, polyvinyl phenol, polyvinylpyrrolidone,chlorinated polybutylene, poly(octadecyl vinyl ether), poly (ethylenevinyl acetate), polyethylene, poly(ethylene oxide)-poly(ethyleneterephthalate), polyethylene/nylon (graft copolymer),polycaprolactones-polyamide (block copolymer), poly(caprolactone)diniethacrylate-n-butyl acrylate, poly(norbornyl-polyhedral oligomericsilsequioxane), polyvinylchloride, urethane/butadiene copolymers,polyurethane-containing block copolymers, styrene-butadiene blockcopolymers, and the like. The polymer(s) used to form the varioussegments in the SMPs described above are either commercially availableor can be synthesized using routine chemistry. Those of skill in the artcan readily prepare the polymers using known chemistry and processingtechniques without undue experimentation.

As will be appreciated by those skilled in the art, conductingpolymerization of different segments using a blowing agent can form ashape memory polymer foam, for example, as may be desired for someapplications. The blowing agent can be of the decomposition type(evolves a gas upon chemical decomposition) or an evaporation type(which vaporizes without chemical reaction). Exemplary blowing agents ofthe decomposition type include, but are not intended to be limited to,sodium bicarbonate, azide compounds, ammonium carbonate, ammoniumnitrite, light metals which evolve hydrogen upon reaction with water,azodicarbonamide, N,N′ dinitrosopentamethylenetetramine, and the like.Exemplary blowing agents of the evaporation type include, but are notintended to be limited to, trichloromonofluoromethane,trichlorotrifluoroethane, methylene chloride, compressed nitrogen, andthe like.

Reference will now be made to reconfigurable pads 14 formed of athermoresponsive SMP, which can take any form (e.g., foam, laminate,solid, composite, and the like). The reconfigurable pad 14 made of theSMP is in its stiff, glassy form at the operating temperatures of thefixture device 10, which is below the lowest thermal transitiontemperature of the SMP. In the training step, the reconfigurable pad 14is heated to a temperature above the thermal transition temperature,which causes the SMP to transition to a polymeric form having lowerstiffness (i.e., decreased flexural modulus properties). Thereconfigurable pad 14 is then pressed against the workpiece 16 with aforce (F₁) and made to deform such that it sufficiently conforms to thecontoured surface of the workpiece 16, as shown in FIGS. 2 and 6.

The reconfigurable pad 14 is then cooled below the thermal transitiontemperature, while still under load (i.e., while holding theconfiguration attained at the end of the previous step) to bring the SMPback to its stiff glassy form. As illustrated in FIGS. 3 and 7, thereconfigurable pad 14 retains the configuration ‘taught’ during thetraining step even after it has cooled down to the regular workingtemperature and is suitable for use to fixture additional workpieces 16.As the stiffness of the SMP reconfigurable pad 14 is higher when the SMPis in its glassy form than when it is in its soft, polymeric form, theclamping force resisted by the reconfigurable pad 14 can be greater thanthe training force.

After a fixturing (i.e., supporting and/or clamping) task is completed,the reconfigurable pad 14 can be reheated to a temperature above thethermal transition temperature and pressed against a workpiece 16 forthe next task so long as the workpieces have similar surface contours,i.e., the reconfigurable pad(s) 14 can proceed directly to the trainingstep shown in FIGS. 2 and 6. However, in some cases it may be necessaryto reset the reconfigurable pad 14 to its original configurationfollowed by a training step before it can be used to support a workpiece16 at a location with a different surface geometry. In the optionalreset step, the reconfigurable pad 14 is unloaded and heated to abovethe thermal transition temperature. The reconfigurable pad 14 is heldunloaded at that temperature (i.e., with the SMP in the soft, polymericform), until the reconfigurable pad 14 has regained its originalconfiguration. Since the SMP reconfigurable pad 14 will have a lowstiffness, shape recovery may be assisted by external means such as byreorienting the reconfigurable pad 14 to use gravity loading. Othermeans of shape recovery assistance can include the use of compressedair, immersion in a fluid, use of another material which opposes the SMPwithin a composite (as will be described below), and the like. When theshape recovery is complete and/or substantially complete, thereconfigurable pad 14 is trained for a new fixturing task.

Composites of a shape memory material and an additional material canalso be employed in the reconfigurable pad 14. As stated above, thecomposite is not intended to be limited to any specific combination ofmaterials. The additional material may be a non-shape memory materialand/or an additional shape memory material. The additional shape memorymaterial may be of the same class (e.g., different shape memorypolymers), or a different class (e.g. a shape memory polymer and a shapememory alloy).

In one embodiment, if the composite comprises a shape memory polymer anda non-shape memory metal or metal alloy, the non-shape memory materialcan be configured to provide an assist mechanism to an SMP to facilitateshape change. As an example, such a composite-containing reconfigurablepad 14 may comprise an element 18 distributed within an SMP matrix 20.The element 18 is depicted as a spring in FIG. 5, but may take any shape(e.g., strip, mesh, honeycomb, and the like). The element 18 provides areturn mechanism for restoring the reconfigurable pad 14 to its originalshape or to the shape of a load under which the reconfigurable pad 14 isplaced.

Optionally, if electrically conducting materials form the element 18,these materials can also be used for resistive or inductive heating toeffect the phase transformation of the SMP itself.

Optionally, element 18 can be formed of a shape memory material (e.g.,an SMA) so as to enable more functionality in the composite. By way ofexample, SMA materials can be selected to be electrically conducting andhave an elastic modulus greater than that of the SMP in both its softand hard forms. Although other common metals, such as steel andaluminum, also possess these properties, these materials have fullyrecoverable strains that are smaller than those for SMA materials (e.g.,less than about 1% for most metals versus about 8% for some SMAmaterials). Therefore, a reconfigurable pad 14 made from an SMA-SMPcomposite can undergo larger fully recoverable deformations than areconfigurable pad 14 made from an SMP composite reinforced with othermetals, provided that the reinforcing component is of the sameconfiguration in both cases. As a consequence, an SMA-SMP compositereconfigurable pad 14 can be configured for a wider variety of fixturingtasks than a composite reconfigurable pad 14 made of SMP and a materialwith a smaller fully recoverable strain than an SMA (e.g., steel,aluminum, and like non-shape memory materials). Despite the advantagesof using SMA over other metals as the second phase in an SMP-basedcomposite, it may be desirable to employ other metals to reduce costs,for example.

In one embodiment, composite reconfigurable pad 14 comprises SMAmaterial distributed throughout a matrix 20 made from the SMP material.The SMA is in close physical (e.g. mechanical and thermal) contact withthe surrounding SMP matrix 20.

As an illustrative example, the compositions of the SMA and SMPconstituents' of the composite can be chosen such that the variouscharacteristic temperatures for these materials are related by:T_(w)<T_(g1)<T_(t)<A_(s)<A_(f)<T_(r)<M_(d), T_(max), wherein T_(w) isthe environmental temperature in which the fixture device 10 is disposedand operated; T_(g1) is the first thermal transition temperature of theSMP; T_(t) is the temperature employed for training (setting is done bycooling to below T_(g1)) of the deformed shape; A_(s) is the austenitestart temperature; A_(f) is the austenite finish temperature; T_(r) isthe temperature employed for recovery of the deformation in theconfigurable pad 14 to its original shape; M_(d) is the temperatureabove which the SMA loses its shape memory properties; and T_(max) isthe lesser of the last transition temperature or the oxidationtemperature for the SMP material. Consequently, the SMA is in itsstress-free martensite phase and the SMP is in its stiff, glassy form atthe regular working or operating temperature of the reconfigurable pad14. Other SMA and SMP compositions could also be used where, forexample, the above temperature relationships do not hold. Therelationship described above is used in the description that follows,but is by no means intended to be limiting.

In the training step, the reconfigurable pad 14 can be resistivelyheated by passing current through the SMA element 18. The heating iscontrolled to raise the temperature of the SMA and the surrounding SMPto T_(t), which is above T_(g1). The SMA continues to be in themartensite phase as T_(t) is also lower than A_(s), at which themartensite to austenite phase transformation is initiated in the SMA. Atthis stage, the SMP is in its soft, polymeric form and the SMA is stillin its lower stiffness martensite phase. The reconfigurable pad 14 isthen contacted with the workpiece 16 in order to deform it to conform tothe workpiece 16. The SMA also deforms along with the SMP, and dependingon the level of stress developed in the SMA, it can undergo eitherelastic deformation (e.g., less than or equal to about 1% strain) aloneor elastic deformation in combination with pseudo-plastic deformation(e.g., up to about 8% strain).

After the reconfigurable pad 14 has achieved sufficient conformance withthe workpiece 16, the setting step is initiated. In this step, thecurrent passing through the SMA is switched off and the reconfigurablepad 14 is allowed to cool down to T_(w), while holding the shape‘taught’ during the training step. External cooling may also be used toaccelerate this step. As the SMP increases its elastic modulus uponcooling, the SMA has elastic, and possibly pseudo-plastic, strain lockedinto it. The SMA element 18 within the SMP matrix 20 is chosen suchthat, for example, the stiffness of its structural form is smaller thanthat of the SMP matrix 20, while in its stiff glassy form. This ensuresthat the elastic part of the strain locked into the SMA element 18 doesnot distort the ‘taught’ shape to any significant extent. Therefore, thereconfigurable pad 14 retains this ‘taught’ shape after the settingprocess is over and the training forces are removed. Maintaining therelative positions of the reconfigurable pad 14 and the workpiece 16throughout the process can ensure the holding of the trained shapeduring the setting process. Alternatively, a constant training force,which depends on the response of the reconfigurable pad 14 during thesetting process, may be used such that the final shape achieved is thedesired one, e.g. the constant force used in the training and settingsteps may yield a surface contour that is different from the desiredone, but the change in the elastic response of the composite pad, as itis cooled below T_(g1), causes the desired final surface to be producedin the pad at T_(w). This is conceptually similar to the over-bendingdone on pressed sheet metal parts to compensate for the change in partgeometry due to elastic ‘springback’.

When the reconfigurable pad 14 is to be reconfigured for fixturing aworkpiece having a different surface contour, it is unloaded and thetemperature increased to T_(t). During this process, the SMP transitionsfrom its stiff, glassy form to a soft, polymeric form, thereby releasingthe elastic strain locked into the SMA during the training and settingsteps. The elastic recovery force provided by the SMA assists the SMP inreverting to its original configuration. The reconfigurable pad 14 canthen be trained for the new workpiece 16. Complete recovery of theoriginal configuration may not be necessary in some cases, and thereconfigurable pad 14 can be trained for the new workpiece 16immediately after it has been heated to T_(t).

If the SMA has undergone any pseudo-plastic strain during thetraining/setting steps and/or the reconfigurable pad 14 needs to berestored to the original configuration before training it for a newworkpiece 16, the heating of the unloaded reconfigurable pad 14 iscontinued until the reset temperature is attained, which is chosen to begreater than A_(f), which is greater than T_(g1). Heating the SMA aboveA_(f) causes the martensite phase to transition to the austenite phase.This phase transition is accompanied by a recovery of the pseudo-plasticstrain. Hence, the SMA reverts to its strain-free originalconfiguration. In some embodiments, there may be some un-recoveredstrain as the number of cycles increases. A significant recovery stressis produced in the SMA during this strain recovery. This stress assiststhe SMP in recovering its original configuration. When the shaperecovery is sufficiently complete, the current flowing through any orall SMA elements 18 is adjusted to a level that brings the temperatureof the reconfigurable pad 14 to T_(t). The reconfigurable pad can now betrained for the next workpiece 16.

Optionally, if the SMA is sheathed in a thermally insulating cover, butcontinues to be in close mechanical contact with the SMP, the shapememory effect can still be used to aid in the shape recovery of thereconfigurable pad 14 during the reset step. The only deviation from theprocedure described above would be that current is not passed throughthe SMA elements for heating. A different heat source would be usedduring the training and reset steps. This results in a less complextemperature relationship (T_(w)<T_(g1)<T_(t)≦T_(r)<T_(max)), whichtranslates into greater freedom in choosing the SMA and SMP components.

In another embodiment, the SMA can be used for resistive heating andsuper-elastic reset. In this embodiment, the super-elastic behavior ofthe SMA component is used to allow the reconfigurable pad 14 to undergolarge deformations during the training step, which are fully recoverableduring the reset step. The elastic recovery forces exerted by thesuper-elastic SMA component help the reconfigurable pad 14 to recoverits original configuration when it needs to be reconfigured forsupporting a workpiece 16 at a location with a different surfacegeometry.

In one embodiment, the reconfigurable pad 14 can comprise an SMA element18 in the austenite phase distributed within an SMP material. The SMPmaterial is in its stiff, glassy form at the regular workingtemperature. The SMA and SMP are in close physical (i.e., mechanical,thermal, and the like) contact; the compositions of which are chosensuch that their characteristic temperatures are related in the followingrelationship: A_(f)<T_(w)<T_(g1)<T_(t)≦T_(r)<M_(d), T_(max).

In the training step, the reconfigurable pad 14 is heated to T_(t),where the SMP transforms into its soft, polymeric form while the SMAremains in its austenite phase. The reconfigurable pad 14 is thenpressed against the workpiece 16 and deformed to make it conform to thesurface contour particular to the workpiece 16. The soft, polymeric SMPdeforms easily and can undergo large strains (e.g. up to 200%).Initially, the SMA deforms elastically, but later if the stress in theSMA material exceeds a critical stress (σ_(m)), the SMA undergoes apseudo-plastic deformation. The SMA can undergo large recoverablestrains (e.g., up to about 8%) at nearly constant stress during thepseudo-plastic deformation, which is associated with a stress-inducedaustenite to martensite phase transformation in the SMA material.

After the desired conformity between the reconfigurable pad 14 and theworkpiece 16 is achieved, the reconfigurable pad 14 is allowed to cooldown to T_(w), while holding the shape ‘taught’ during the trainingstep. Other cooling methods (e.g., air jet) may be used to assist and/oraccelerate the cooling process as desired. When the temperature dropsbelow T_(g1), the SMP transforms into its stiff, glassy form, therebylocking the strain (elastic and, possibly, pseudo-plastic) in the SMA.As discussed earlier, the SMA element 18 within the SMP matrix 20 can bechosen such that its stiffness is smaller than that of the SMP matrix 20in its stiff glassy form. Consequently, the reconfigurable pad 14retains the ‘taught’ shape at T_(w) and is ready for use.

When the reconfigurable pad 14 needs to be reconfigured to supportanother surface, it is unloaded and heated to T_(r), which is aboveT_(g1). As the elastic modulus of the SMP decreases, the elastic andpseudo-plastic strain locked into the SMA is gradually recovered. TheSMA exerts elastic restoring forces on the surrounding SMP that canassist the SMP in recovering its original configuration. It should benoted that recovery of the original configuration is optional and, insome embodiments, the reconfigurable pad 14 can be directly taken to thetraining step for the next workpiece 16 after it has been heated to Tr.

In yet another embodiment, the SMA can be adapted for heating,actuation, and reset. In this embodiment, at the regular working oroperating temperature, the reconfigurable pad 14 comprisespseudo-plastically strained SMA material in the martensite phasedistributed within a stiff, glassy SMP matrix. The SMA and SMPcomponents of the reconfigurable pad 14 are in close physical contact(e.g. mechanical, thermal, and the like) and their composition is chosensuch that the characteristic temperatures are related as follows:T_(w)<T_(g1), M_(f)<T_(t)≦T_(r)<A_(s)<T_(a), A_(f)<T_(max), M_(d). Inthis embodiment, the composite includes at least two different SMAelements 18 and 22, shown in FIG. 5, wherein SMA element 18 is selectedto be antagonistic to SMA element 22. That is, SMA element 18, onactuation, will seek to deform the SMP matrix 20 in a direction oppositeto that of the element 22. SMA elements 18 and 22 are distributedthroughout the SMP matrix 20.

In the training step, the reconfigurable pad 14 is heated to T_(t),which is greater than T_(g1). As a consequence, the SMP transitions toits soft, polymeric form. However, the SMA remains in the martensitephase because T_(t) is lower than A_(s), at which the martensite toaustenite phase transition is initiated in the SMA. A subset of the SMAelements 18 and/or 22 in the reconfigurable pad 14 is selectivelyactuated by heating the subset such that these elements are heated totheir actuation temperature. Heating the selected subset of thepre-strained martensite phase SMA elements above A_(s) initiates themartensite to austenite phase transition in these elements. As aconsequence of this transformation, the activated SMA elements 18 and/or22 attempt to revert to their strain-free configuration and, in thisprocess, exert force on the surrounding SMP matrix 20 and other SMAelements 18 and/or 22. Note that the strain-free configuration for theSMA elements is not the same as the configuration of these elements inthe original configuration of the reconfigurable pad 14 because the SMAelements are pre-strained in the latter configuration. The elements 18and/or 22 forming the actuated subset are chosen such that, as aconsequence of actuating this subset, the reconfigurable pad 14 deformsinto a geometry that is suitable for fixturing the given workpiece 16.

While it may be desirable to achieve the required geometry entirely byusing SMA actuation, an assist can also be provided to fine tune thedesired final geometry. For example, a further mechanical step, in whichthe partially trained reconfigurable pad 14 is pressed against atraining surface at a temperature above T_(g1), may be used. This isespecially desirable if close tolerances are desired on the contouredsurface. The work required in the mechanical training step is less inthis case than if the entire deformation of the reconfigurable pad 14was to be done by pressing the reconfigurable pad 14 against thetraining surface. As the SMP material is in its soft, polymeric form,the actuation force obtained from the SMA elements can easily deform it.The non-actuated SMA elements, which are in the martensite phase,undergo pure elastic deformation initially, but can deformpseudo-plastically if the stress in these elements exceeds the firstyield stress of the martensite phase. The elastic deformation is limitedto small fully recoverable strains (e.g., less than about 1%), but thepseudo-plastic deformation can accommodate much larger fully recoverablestrains (e.g., up to about 8%).

After the reconfigurable pad 14 conforms sufficiently to the trainingsurface (e.g., workpiece 16), it is cooled to T_(w) while holding theconfiguration attained at the end of the training step. This is achievedfor example by switching off a current passing through only those SMAelements that are not actuated in the training step. Other cooling meansmay also be used to assist and/or accelerate this process. The actuationcurrent passing through the actuated SMA elements may be adjusted inkeeping with the changing modulus of the SMP matrix such that thesurface contour ‘taught’ during the training step is reasonablyunchanged until the bulk of the SMP material has transformed back to itsstiff, glassy form. The actuation current is then switched off and theactuated elements are cooled down to T_(w). The ‘taught’ shape is heldduring the secondary mechanical training step, if used, by maintainingthe relative position of the training surface until the SMP hasglassified. Other alternatives discussed earlier to hold the ‘taught’shape during the setting step can also be used. At the end of thesetting process, the reconfigurable pad 14 retains the shape ‘taught’during the training step and is ready for use. In this condition, theSMA elements (actuated or not) have some elastic, and possibly somepseudo-plastic strain.

When the reconfigurable pad 14 needs to be reconfigured for anotherworkpiece 16, it can be heated to T_(r). During this process, the SMPmaterial transforms into its soft, polymeric form as T_(r) is greaterthan T_(g1). The elastic strain locked in the SMA elements (actuated ornot) is gradually released during the softening of the SMP. Theaccompanying elastic recovery forces help in restoring thereconfigurable pad 14 to the original configuration. If completerecovery of the original shape is not desired, the heated reconfigurablepad 14 can be directly trained for the next workpiece 16.

In the event that the shape recovery obtained in the above process isinsufficient for the reconfigurable pad 14 to be trained for a newworkpiece 16, the shape recovery process can be continued. If any SMAelements have undergone pseudo-plastic deformation during thetraining/setting steps, that strain cannot be recovered by heating thereconfigurable pad 14 to T_(r). In this case, the set of SMA elements(20 or 22), which are antagonistic to those actuated in the trainingstep, is actuated while the reconfigurable pad 14 is held at T_(r). Theactuation force exerted on the reconfigurable pad 14 by these elements(20 or 22), as they undergo the martensite to austenite phase transitionhelps the reconfigurable pad 14 recover its original configuration.After the shape recovery is sufficiently complete, the reconfigurablepad 14 can be trained for the next workpiece 14.

In yet another embodiment, the SMA can be adapted to provide heating,actuation and reset by means of a two-way shape memory effect. In thisembodiment (see FIG. 5), at the working temperature, the reconfigurablepad 14 comprises SMA element 18 distributed within the stiff, glassy SMPmatrix 20. The SMA material is in the martensite phase and has beenprocessed to allow the SMA element 18 to ‘remember’ two shapes: a hightemperature shape, which is the natural shape of the element when theSMA is fully austenitic; and a low temperature shape, which is thenatural shape when the material is fully martensitic. The SMA and SMPmaterials are in close physical (e.g., mechanical, thermal) contact andtheir composition is chosen such that the characteristic temperaturesare related as follows:T_(w)<M_(f)<M_(s)<T_(g1)<T_(t)≦T_(r)<A_(s)<T_(a)≦A_(f)<T_(max),M_(d).

In the training step, the reconfigurable pad 14 is heated to T_(t),which is greater than T_(g1). As a consequence, the SMP transitions toits soft, polymeric form. The reconfigurable pad 14 can be heated, forexample, by passing current through all of the SMA elements 18. Otherheating methods may also be used to assist and/or accelerate the heatingprocess. A subset of the SMA elements 18 in the reconfigurable pad 14can then be actuated by heating them to the appropriate actuationtemperature. This selective actuation can be obtained, for example, byincreasing the current passing through those elements 18. Heating themartensite phase SMA elements 18 to a temperature above A_(s) initiatesa martensite to austenite phase transition in those elements 18. As aconsequence of this transformation, the actuated SMA elements 18 try toattain their high temperature shape, and in the process exert force onthe surrounding SMP matrix 20 and other SMA elements 18. The elements 18forming the actuated set are chosen such that actuating this set deformsthe reconfigurable pad 14 into a geometry that is suitable for the givenworkpiece 16.

While it is desirable to achieve the required geometry entirely by usingSMA actuation, it is only necessary that the actuation achieve ageometry that is in the neighborhood of the desired one. A furthermechanical step, in which the partially trained reconfigurable pad 14 ispressed against a training surface at a temperature above T_(g1), may beused to obtain the geometry necessary for the given workpiece 16. Thework required in the mechanical step is less in this case than if theentire deformation of the pad were to be done by pressing thereconfigurable pad 14 against the training surface. As the SMP materialis in its soft, polymeric form, the actuation force obtained from theSMA elements 18 can easily deform it. The non-actuated SMA elements 18remain in the martensite phase throughout the training process andundergo purely elastic deformation initially, but can deformpseudo-plastically if the stress in these elements 18 exceeds the firstyield stress of the martensite phase. The elastic deformation is limitedto small fully recoverable strains (e.g., less than about 1%), but thepseudo-plastic deformation can accommodate larger fully recoverablestrains (e.g., up to about 2%).

After the reconfigurable pad 14 conforms sufficiently to the trainingsurface with the desired geometry, it is cooled to T_(w), while holdingthe configuration attained at the end of the training step. This isachieved, for example, by switching off the current passing through onlythose SMA elements 18 that are not actuated in the training step. As inthe various other embodiments, alternative cooling means may also beused to assist and/or accelerate this process. The actuation currentpassing through the actuated SMA elements 18 is adjusted to prevent orminimize the deviation of the surface from the ‘taught’ shape until thebulk of the SMP material has transformed back to its stiff, glassy form.This may result in the temperature of these elements 18 remaining aboveA_(f), and hence the actuated elements 18 continue to strive to attaintheir high temperature shape, while the bulk of the SMP matrix 20 isglassifying. The actuation current is then switched off and the actuatedelements 18 are cooled down to T_(w). The ‘taught’ shape is held bykeeping the elements 18 actuated, and if a secondary mechanical trainingstep is used, by keeping the reconfigurable pad 14 pressed against thetraining surface until the SMP has glassified. When the temperature ofthe actuated SMA elements 18 drops below the martensite-starttemperature (M_(s)) during the cooling process, the austenite in the SMAbegins to transform to martensite. This transformation is accompanied bythese elements attempting to revert back to their low temperature shape.However, as M_(s)<T_(g1), the surrounding SMP matrix 20 has glassifiedbefore the austenite to martensite phase transformation and theassociated shape change can take effect. Consequently, thereconfigurable pad 14 retains the shape ‘taught’ during the trainingstep at the conclusion of the setting process and is ready for use. Inthis condition, the SMA elements 18 (actuated or not) have some elastic,and possibly some pseudo-plastic, strain locked therein.

When the reconfigurable pad 14 needs to be reconfigured for supporting aworkpiece 16 at a location with a different surface geometry, the padcan be heated to the T_(r) by passing current through all of the SMAelements 18, for example. As T_(r) is greater than T_(g1), the SMPmaterial transforms into its soft, polymeric form. The elastic strainlocked in the SMA elements (actuated or not) is gradually releasedduring the softening of the SMP. The accompanying elastic recoveryforces help in restoring the pad to its original configuration.

As described above, complete recovery of the original shape is notnecessary, and the heated reconfigurable pad 14 can be trained for thenext fixturing task after the SMP matrix 20 has softened sufficiently.In the event that the shape recovery obtained in the above process isinsufficient, the shape recovery process needs to be continued. If anySMA elements 18 have undergone pseudo-plastic deformation during thetraining and setting steps, that strain cannot be recovered by simplyheating the reconfigurable pad 14 to T_(r). In this case, the SMAelements 18 that have undergone pseudo-plastic deformation are heated tothe actuation temperature (e.g., by increasing the current passingthrough these elements), while the rest of the reconfigurable pad 14 isheld at about T_(r). In doing this, the elements 18 are able to undergothe martensite to austenite phase transition, and their temperature cansubsequently be reduced to T_(r). The reconfigurable pad 14 is now readyto be reconfigured for the next fixturing task.

Although reference has been made to using an electric current to heatthe shape memory material of the reconfigurable pad 14 of the fixturedevice 10, various other methods can be employed to effect thetemperature changes used for the various phase transformations describedabove. For example, heating of the reconfigurable pad 14 can be effectedby dipping or exposing it or the entire fixture device 10 to heatedfluids (liquids and/or gasses); by inductive heating when electricallyconductive materials are employed; by exposing it to incident laserlight; by thermoelectric heating; by microwave heating; by infraredheating; by flash lamps; and the like. In a similar manner, variousmeans of cooling the reconfigurable pad 14 include, but are not intendedto be limited to, dipping or exposing the reconfigurable pad 14 or theentire fixture device 10 to cooled fluids; thermoelectric cooling; andthe like.

Alternatively, to increase heating and cooling transfer efficiency twofixture devices 10 can be employed, wherein one fixture device 10 is ina so-called “stand-by” mode (or trained for a second workpiece 16) andthe other is employed for a given workpiece 16. Still further, differenttypes of SMA elements 18 and/or 22 can be employed wherein one subset ofelements 18 (or 22) has a different phase transformation temperaturethan the other subset of elements 22 (or 18).

Reference will now be made to use of a thermoelectric device for heatingand/or cooling the reconfigurable pad 14 of the fixture device 10. Athermoelectric device is a solid-state electronic component that canemit or absorb heat upon the passage of a current across the device, orvice versa. To generate heat differences, a thermoelectric device relieson the Peltier effect, which occurs when a current is passed through apair of dissimilar conductors connected in a closed loop. The currentdrives a transfer of heat from one junction of the two dissimilarconductors to the other. The conductors, which can be semiconductors,metals, ionic conductors, or the like, attempt to return to the chargeequilibrium that existed before the current was applied by absorbingenergy at one junction and releasing it at the other (i.e., one junctioncools off while the other heats up). Additional couples (pairs ofdissimilar conductors) can be connected in series to enhance thiseffect. The direction of heat transfer is controlled by the polarity ofthe current, (i.e., reversing the polarity will change the direction oftransfer and thus whether heat is absorbed or emitted).

An exemplary thermoelectric device comprises an array of couplessandwiched between two substrates. Each couple comprises one n-type andone p-type semiconductor. The couples are configured such that they areconnected electrically in series, and thermally in parallel. The twosubstrates, which provide the platform for the connected couples, may bemetals or metallized ceramics to facilitate heat transfer. Athermoelectric device may function singularly or in groups with series,parallel or series/parallel electrical connections depending on thedesired level of heat transfer needed to activate the particular shapememory material of the reconfigurable pad 14.

The same semiconductor composition can be doped to form both members ofthe couple or two different semiconductor compositions can be used. Agood semiconducting thermoelectric material is measured by its “figureof merit” or ZT, wherein T is the temperature and Z is defined as:Z=S ² /ρKwherein S is the Seebeck coefficient (ratio of the open-circuit voltageto the temperature difference between the hot and cold junctions of acircuit), ρ is the electrical resistivity, and K is the thermalconductivity. Desirably, the semiconductor has a ZT greater than orequal to about 0.5 at the given training temperature for the particularshape memory material used in the reconfigurable pad 14. Semiconductingmaterials suitable for use with the fixture devices disclosed hereininclude alloys of lead, bismuth, and/or antimony with tellurium and/orselenium (e.g., Bi₂Te₃, PbTe, SbTe, BiSb, Bi_(1.5)Sb_(0.5)Te₃, PbSeTe,and the like); CsBi₄Te₆; SiGe; MnTe; filled skudderudites (e.g.,CeFe₄Sb₁₂ and the like); XeIr₄Sb₁₂, Sr₈Ga₁₆Ge₃₀; Chevrel compounds(e.g., Cu_(3.1)Mo₆Se₈, Cu_(1.38)Fe_(0.66)Mo₆Se₈, and Ti_(0.9)Mo₆Se₈, andthe like); and the like. One skilled in the art in view of thisdisclosure can determine which compositions would be appropriate for usein the fixture device 10 based on the particular shape memory materialsof the reconfigurable pad 14. For example, Bi₂Te₃ has a ZT of 1.0 at 300degrees Kelvin (K) and PbTe has a ZT of 0.9 at 500 K, both of which maybe used with an SMP- or SMA-based reconfigurable pad 14.

A fixture device 10 incorporating a thermoelectric unit in operativecommunication with the reconfigurable pad 14 is shown in FIG. 8. Thethermoelectric unit 24 is interposed between the base member 12 and thereconfigurable pad 14. A controller (e.g., a power supply) 28 is inelectrical communication with the thermoelectric unit 24. Optionally,the controller 28 may include a temperature-measuring device (e.g., athermocouple) in operative communication with the thermoelectric unit 24and/or the reconfigurable pad 14 as a means of providing feedback to thecontroller 28.

An optional adhesion layer 26 may be used to further improve the bondingstrength between the reconfigurable pad 14 and the thermoelectric unit24. Suitable materials for use in the adhesion layer 26 includeelectrically conductive polymer adhesives, metallic films (e.g.,titanium, chromium, alloys comprising titanium or chromium, and thelike), organosilane compounds, and the like.

In operation of a fixture device 10 that makes use of a thermoelectricunit 24, a current is passed through the thermoelectric unit 24 in afirst direction effective to heat the shape memory material of thereconfigurable pad 14 to the training temperature. The reconfigurablepad 14 is then pressed against the workpiece 16 with a force (F₁) andmade to deform such that it sufficiently conforms to the contouredsurface of the workpiece 16, as shown in FIGS. 2 and 6.

The reconfigurable pad 14 is then cooled below the training temperatureby reversing the direction of the current passed through thethermoelectric unit 24. At this point, as illustrated in FIGS. 3 and 7,the reconfigurable pad 14 retains the configuration ‘taught’ during thetraining step even after it has cooled down to the regular workingtemperature and is suitable for fixturing workpieces 16 having thetrained configuration. The next training step, or a reset step, can becarried out by passing a current through the thermoelectric unit 24 inthe first direction again effective to heat the shape memory material ofthe reconfigurable pad 14 to the training temperature.

In an advantageous feature of using a thermoelectric unit 24, atemperature gradient in the shape memory material may be established(e.g., by reversing the direction of the current), while it is in theheated state (i.e., at or above the training temperature) but before thereconfigurable pad 14 is brought in contact with the training surface.This temperature gradient desirably results in a higher temperature onthe surface of the reconfigurable pad 14 to be trained, and a lowertemperature on an inner (i.e., interior to the surface to be trained)portion. In this manner, the colder portion of the shape memorymaterial, and thus the reconfigurable pad 14, retains its shape andrigidity while the hotter portion is trained under compression. Thetemperature gradient permits appropriate temperature control, which canbe beneficial if the reconfigurable pad 14 and training surface havedifferent thermal masses and temperatures. For example, establishing thetemperature gradient can help prevent melting or delamination/separationof a shape memory polymer reconfigurable pad 14 from the base member 12.

Another fixture device 10 incorporating a thermoelectric unit 24 isshown in FIG. 9. The fixture device 10 includes a chamber 30 interposedbetween the reconfigurable pad 14 and the base member 12. The chamber 30includes an inlet 32 (in this embodiment two inlets 32 and 34) and anoutlet 36 through which air may flow. The thermoelectric unit 24, whichis in electrical communication with the controller 28, is disposedinside the chamber such that two portions are defined by thethermoelectric unit 24. On one side of the thermoelectric unit 24 is aheat sink 38, and on an opposite side of the thermoelectric unit is acold sink 40. The heat sink 38 and the cold sink 40 are downstream ofthe inlets 32 and 34. The reconfigurable pad 14 is disposed on thechamber outlet 36.

In operation of the fixture device 10 shown in FIG. 9, a current ispassed through the thermoelectric unit 24 effective to heat the heatsink 38 (and in turn cool the cold sink 40). Air, which is forcedthrough the chamber 30 via chamber inlet 32, is heated by the heat sink38 and exits the chamber outlet 36 where it contacts the reconfigurablepad 14. Once the shape memory material of the reconfigurable pad 14 isheated to the training temperature, the reconfigurable pad 14 can bepressed against the workpiece 16 with a force (F₁) and made to deformsuch that it sufficiently conforms to the contoured surface of theworkpiece 16, as shown in FIGS. 2 and 6.

The reconfigurable pad 14 is then cooled below the training temperaturewhile still under F₁. The reconfigurable pad 14 can be naturally cooledby shutting off the air supply to the chamber inlet 32 and discontinuingthe current passing through the thermoelectric unit 24. Alternatively,the reconfigurable pad 14 can be cooled by shutting off the air supplyto chamber inlet 32, and forcing air through the chamber 30 via chamberinlet 34 where it is cooled by the cold sink 40 and exits the chamberoutlet 36 to contact the reconfigurable pad 14. At this point, asillustrated in FIGS. 3 and 7, the reconfigurable pad 14 retains theconfiguration ‘taught’ during the training step even after it has cooleddown to the regular working temperature and is suitable for fixturingworkpieces 16 having the trained configuration. The current passingthrough the thermoelectric unit 24 and any air flowing through thechamber 30 can be discontinued after the training step. Subsequenttraining steps can be performed in a similar fashion.

In one embodiment, the fixture device 10 may further comprise a valve(e.g., a check valve or a flapper valve) 42, which is downstream of thethermoelectric unit 24, heat sink 38, and cold sink 40. The valve canprevent air, while being forced through the chamber 30, from flowinginto one inlet, across the chamber, and out through the other inlet.

In another embodiment, the fixture device 10 may further comprise aperforated plate 44 disposed between the chamber outlet 36 and thereconfigurable pad 14. The perforated plate 44 provides an additionalsupport structure for the reconfigurable pad 14 to rest upon, whilepermitting air to flow from the chamber 30 to heat or cool thereconfigurable pad 14.

While the disclosure has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims.

1. A process, comprising: contacting a surface of at least one workpiecewith a reconfigurable pad of a fixture device, wherein thereconfigurable pad comprises a shape memory material configured toconform to the surface of the at least one workpiece; and fixturing thecontacted workpiece.
 2. The process of claim 1, further comprisingconforming the reconfigurable pad of the fixture device to the surfaceof the at least one workpiece prior to the contacting.
 3. The process ofclaim 2, wherein the conforming comprises: activating the shape memorymaterial; applying a force to the reconfigurable pad effective to deformthe reconfigurable pad from an original shape to a shape conforming tothe surface of the workpiece or a training surface; and deactivating theshape memory material.
 4. The process of claim 3, wherein activating theshape memory material comprises applying at least one of heat, moisture,and light to the shape memory material, and wherein deactivating theshape memory material comprises discontinuing the at least one of theheat, the moisture, and the light.
 5. The process of claim 4, whereinapplying the heat comprises resistive heating, contacting a heatedfluid, inductive heating, microwave heating, exposing to laser light,thermoelectric heating, microwave heating, infrared heating, exposing toa flash lamp, convective heating, or a combination comprising at leastone of the foregoing.
 6. The process of claim 4, wherein deactivatingthe heat comprises removing a heating source, free convective fluidcooling, forced convective fluid cooling, contacting a cooled fluid,thermoelectric cooling, or a combination comprising at least one of theforegoing.
 7. The process of claim 1, further comprising resetting thereconfigurable pad to the original shape after the fixturing.
 8. Theprocess of claim 1, further comprising resetting the reconfigurable padto a different shape corresponding to a surface of at least onedifferent workpiece.
 9. The process of claim 7, wherein the resettingcomprises activating the shape memory material without an applied load.10. The process of claim 1, wherein the fixturing comprises supportingthe workpiece in a fixed position.
 11. The process of claim 1, whereinthe contacting comprises disposing the workpiece between thereconfigurable pad of the fixture device and an other pad of the fixturedevice, and the fixturing comprises clamping the workpiece in a fixedposition.
 12. The process of claim 11, wherein the other pad of thefixture device comprises a shape memory material configured to conformto another surface of the at least one workpiece.
 13. The process ofclaim 11, further comprising conforming the other pad of the fixturedevice to the other surface of the workpiece prior to the contacting.14. The process of claim 1, further comprising using a locating pin toprovide information regarding location of the workpiece.
 15. A process,comprising: contacting a first surface of a first workpiece with areconfigurable pad of a fixture device, wherein the reconfigurable padcomprises a shape memory material configured to conform to the firstsurface of the first workpiece; fixturing the contacted first workpiece;conforming the reconfigurable pad of the fixture device to a secondsurface of a second workpiece; contacting the second surface of thesecond workpiece with the reconfigurable pad of the fixture device; andfixturing the second workpiece.
 16. The process of claim 15, furthercomprising resetting the reconfigurable pad to an original shape priorto conforming.
 17. A process for conforming a reconfigurable pad of afixture device to a surface of at least one workpiece, the processcomprising: heating the reconfigurable pad effective to increase atemperature of a shape memory material to or above a shape settingtemperature; applying a force to the reconfigurable pad effective todeform the reconfigurable pad from an original shape to a shapeconforming to the surface of the at least one workpiece; and cooling theshape memory material below the shape setting temperature.
 18. Theprocess of claim 17, wherein the heating comprises resistive heating,contacting a heated fluid, inductive heating, microwave heating,exposing to laser light, thermoelectric heating, microwave heating,infrared heating, exposing to a flash lamp, convective heating, or acombination comprising at least one of the foregoing.
 19. The process ofclaim 17, wherein the applying comprises contacting the workpiece to theheated reconfigurable pad.
 20. The process of claim 17, wherein theapplying comprises contacting a master article with a shapesubstantially similar to the workpiece to the heated reconfigurable pad.21. The process of claim 17, wherein the cooling comprises removing aheating source, free convective fluid cooling, forced convective fluidcooling, contacting a cooled fluid, thermoelectric cooling, or acombination comprising at least one of the foregoing.